The diagnosis of unclassified leukodystrophies remains a challenge for the clinical neurologist. The leukodystrophy Childhood Onset Ataxia and Central Hypomyelination (CACH), also known as Vanishing White Matter Disease (VWM), both hereinafter referred to as CACH/VWM, is a fatal brain disorder caused by mutations in any one of the five subunits of the eukaryotic initiation factor 2B (eIF2B) (van der Knaap, MS et al, Ann Neurol 2002, 1, 264). This initiation factor is essential for protein synthesis and regulates translation in response to cellular stresses. CACH/VWM is though to be one of the most frequent etiologies of undiagnosed leukodystrophy.
Its diagnosis currently requires the recognition of frequently variable clinical features, magnetic resonance imaging findings that are not always specific for the disease, and sequencing of the 57 exons of the eIF2B genes associated with the disease (Leegwater. PA et al. Nat Genet 2001; 29:383); Schiffmann, R, et al. Gene Reviews. 2003-2005, www.genetests.org). This may delay or prevent accurate diagnosis in many cases.
A report has proposed elevation of cerebrospinal fluid (CSF) glycine as a biomarker for the VWM leukoencephalopathy (van der Knaap, MS et al., J Child Neurol 1999; 14:728). As stated by the authors, the elevations in glycine were moderate at most, and not present in all VWM patients. Most importantly, elevations in CSF glycine are observed in other neurodegenerative disorders, and thus are not specific for CACH/VWM. Do you want me to add the other references here?
CSF is a relatively accessible patient tissue, which has historically been used to investigate neurologic disorders of infectious, inflammatory, neoplastic and degenerative etiology. To a certain degree, CSF is shielded from non-neurologic protein sources by the blood-cerebrospinal fluid barrier and has a relatively slow protein turn-over. Its close contact with the brain's extracellular space makes it a very attractive source to search for biomarkers associated with neurologic disorders.
As a result of the development of effective approaches for proteome analysis, an increasing number of candidate biomarkers have been recently identified in the CSF of patients with neurologic disorders, including amyotrophic lateral sclerosis (Ramstrom M etal. Proteomics 2004;4:4010), multiple sclerosis (Dumont D et al., Proteomics 2004;4:2117), Creutzfeld Jacob disease (Sanchez JC et al. Proteomics 2004;4:2229), and adult degenerative disorders such as Alzheimer's disease (Zhang J et al. J Alzheimers Dis. 2005;7:125). Most of these studies used either the conventional two dimensional gel electrophoresis (2-DG)/mass spectrometry (MS) approach, or shotgun proteomic approaches in combination with clustering analyses (Aebersold R et al., Nature 2003;422:198). Thus, proteomics is emerging as a reliable tool to screen for disease associated biomarkers (Domon B, et al. J Proteome Res 2004;3:253; Marko-Varga G, et al. J Proteome Res 2004;3:167), but as yet has had only limited application to pediatric degenerative central nervous system disorders such as CACH/VWM.
A rapid, clinically available diagnostic test for this disorder is, therefore, highly desirable and, before this, unknown. We have discovered such a biochemical marker and have devised a diagnostic test for it in CSF that is rapid (48 hrs.) and produces unequivocal results.